A rotary shaft position indicating switch assembly can be mounted on a valve or a hydraulic or pneumatic valve actuator having a rotary shaft projecting therefrom whose position is to be telemetered to a remote location. A rotary shaft position switch can be used for telemetering the positioning of a rotatable shaft, such as on a flow control valve to a remote location for indicating whether that valve is opened or closed. Often times these rotary shaft position indicators need to be used within explosive atmospheres.
An explosive atmosphere can be a mixture of dangerous substances with air, under atmospheric conditions, in the form of gases, vapors, mist, or dust in which, after ignition has occurred, combustion spreads to the entire unburned mixture. Atmospheric conditions are commonly referred to as ambient temperatures and pressures. That is to say temperatures of −20° C. to 40° C. and pressures of 0.8 to 1.1 bar.
Many workplaces may contain or have activities that produce explosive or potentially explosive atmospheres. Examples include places where work activities create or release flammable gases or vapors, such as vehicle paint spraying, or in workplaces handling fine organic dusts such as grain flour or wood.
These explosive atmosphere areas must be protected from sources of ignition. Employers are often required to take action to assure the safety of their employees, such as requiring employees wear appropriate clothing that does not create the risk of an electrostatic discharge igniting the explosive atmosphere, e.g., anti-static footwear. The clothing provided depends on the level of risk identified in the risk assessment.
The employer must also insure that the equipment within the explosive atmosphere meets certain requirements such as the Potentially Explosive Atmospheres (ATEX) Directive 94/9/EC which provides the technical requirements to be applied to equipment intended for use in potentially explosive atmospheres. Preventing releases of dangerous substances, which can create explosive atmospheres, and preventing sources of ignition are two widely used ways of reducing the risk. The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) place duties on employers to eliminate or control the risks from explosive atmospheres in the workplace.
It would be desirable to have a rotatable shaft position indicator that can be used within an explosive environment or volatile atmosphere. As part of this desire, it would be nice to have a rotatable shaft position indicator that is thoroughly grounded to remove electrical potential. And, it would be desirable to have a rotatable shaft position indicator that can be used for extended periods of time without seizing up and needing repair or replacement.